The present invention relates to a circuit breaker, such as a wiring breaker or an earth leakage breaker, in which a switch mechanism and an overcurrent tripping device are incorporated in a molded container, and in particular, to a circuit breaker with a completely electromagnetic type overcurrent tripping device.
FIG. 12 is a vertical cross sectional view of a conventional example of a three-pole circuit breaker (earth leakage breaker). In FIG. 12, the circuit breaker is integrally formed in a molded container consisting of a case 1 and a cover 2. In the ON-condition of the circuit breaker as shown in the figure, a current path is formed of a fixed contact 4 integral with a power terminal 3; a movable contact 5 that contacts the fixed contact 4 via a fixed contact point 4a and a movable contact point 5a; a flexible lead 6, one end of which is connected to the movable contact 5 by spot welding; a lead plate 7 to which the other end of the lead 6 is connected by spot welding; a relay plate 9 to which the lead plate 7 is tightened with a screw 8; a coil 11 of the overcurrent tripping device 10, one end of which is connected to the relay plate 9 by soldering; and a load terminal 12 to which the coil 11 is connected by soldering. The lead for each pole penetrates through a zero-phase current transformer (ZCT) 13, and causes a secondary output to be produced in the ZCT 13 when a leakage occurs. A leakage detection circuit for amplifying the secondary output to output a tripping signal is mounted on a print board 14, and a power line 15 from the print board is spot-welded to the lead plate 7 together with the lead 6.
The movable contact 5 is rotatably retained at the right end of FIG. 12, and subjected to a clockwise force by a contact spring 16 formed of a compression spring, while the movable contact 5 is also pressed downward onto the fixed contact 4 by a switch mechanism 17. The switch mechanism 17 is explained in brief. The switch mechanism 17 comprises a handle 19 supported by the case 1 via a support shaft 18; a link 20 to which one end of an arm 19a of the handle 19 is coupled; a pressing rod 21, one end of which is connected to the other end of the link 20 and the other end of which contacts the movable contact 5 and is guided in a vertical sliding motion, as in FIG. 12, along a groove in the case 1; a latch 22, one end of which is coupled to the support shaft 18; and a link 23 that connects the latch 22 and the link 20 together.
In the condition that the circuit breaker is turned on as shown in the figure, the link 20 is subjected to a clockwise rotating force via the pressing rod 21 under the force of the contact spring 16, while the latch 22 is simultaneously subjected to a clockwise rotating force via the link 23, with its tip locked by a claw 24a of a trip bar 24 to prevent its rotation. The trip bar 24 is rotatably supported by the case 1 via an insulating bar 24b that extends over each pole, and a tripping arm 24c is provided so as to correspond to the overcurrent tripping device 10 for each pole. The claw 24a is integrally installed opposite to the tripping arm 24c of a central pole.
FIG. 13 is a side view for showing the completely electromagnetic type overcurrent tripping device 10. In FIG. 13, an oil dash pot 26 inserted into the coil 11 is coupled by soldering to one leg of a yoke 25 formed of a magnetic plate bent like the character "L" in such a way that the oil dash pot penetrates through the yoke 25, with an armature 27 rotatably supported by the tip of the other leg of the yoke. The armature 27 is held by a return spring 28 installed between the armature 27 and the yoke 25 as shown in the figure, and is opposed to an electromagnetic pole 29 at the head of the oil dash pot 26. One end of the coil 11 penetrates through the yoke 25 and is soldered to the relay plate 9, whereas the other end is soldered to the load terminal 12. The oil dash pot 26 adjusts a tripping operation time in a well known manner, and comprises a non-magnetic cylinder, in which an oil is filled and in which a plunger is sealed together with a braking spring.
The main circuit section of the circuit breaker is assembled as follows. The lead 6 is connected to the movable contact 5, and the lead plate 7 with the power line 15 connected thereto is connected to the other end of the lead 6. The movable contact 5 is installed into the case 1 with the fixed contact 4 attached thereto, the lead 6 is passed through the ZCT 13, and the lead plate 7 is fitted and held in a groove (not shown) in the case 1. Then, the relay plate 9 of the overcurrent tripping device 10 assembled as shown in FIG. 13 is placed on the lead plate 7, and the screw 8 is applied in a screw hole (not shown) in the relay plate 9 through a through hole (not shown) in the lead plate 7. The screw 8 is tightened from the bottom of the case 1 (the bottom of FIG. 12) via a window hole (not shown). The other end of the power line 15 is subsequently soldered to the print board 14.
In this circuit breaker, when the tip 19b of the handle 19 is rotated from the ON state shown in FIG. 12 to the position shown by the broken line, the pressing rod 21 is raised via the link 20 to cause the movable contact 5 to be opened to the position shown by the broken line, under the action of the contact spring 16, i.e. OFF operation.
On the other hand, when a main circuit current becomes excessive and thus the armature 27 is attracted to the electromagnetic pole 29, the trip bar 24 is rotated in a counterclockwise direction via the tripping arm 24c, thereby releasing the latch 22 locked by the claw 24a to rotate the latch in the clockwise direction. Consequently, the link 23 is displaced to the position shown by the broken line, while the pressing bar 21 is simultaneously raised to open the movable contact 5 (tripping operation). If leakage occurs to cause the main circuit current to become unbalanced, a secondary output is generated by the ZCT 13, causing a tripping signal to be sent out from the earth leakage detection circuit to a tripping coil unit (not shown). The tripping coil unit causes the trip bar 24 to be driven to generate a tripping operation.
These conventional circuit breakers have the following problems.
(1) The coil of the overcurrent tripping device is changed depending on the rated current. Since, however, the yoke and the oil dash pot are soldered and coupled together via the coil, the use of the yoke and oil dash pot common to different rated currents is limited by the coil (the rate current), resulting in an inflexible production schedule.
(2) Since the overcurrent tripping device is screwed and fixed to the case for each pole, a large amount of time and labor is required to assemble the circuit breaker.
(3) Since the main circuit conductor or lead is disposed in the lower part of the overcurrent tripping device, it must be connected to an overcurrent tripping device from the rear side of the case, thereby degrading workability. Connection of the power line to the earth leakage detection circuit also degrades workability.
It is thus an object of this invention to solve these problems by providing a circuit breaker incorporating in a molded container formed of a case and a cover, a switch mechanism; and an overcurrent tripping device that acts on a latch for the switch mechanism to generate a tripping operation and in which an oil dash pot inserted into a coil is combined with an L-shaped yoke supporting an armature and a return spring.